goto evga.com->community->message boards->780i
There is likely a motherboard BIOS update which will fix your problem - follow the instructions and make sure you do it correctly or you may cause damage to your motherboard.
I use a 750I - and the fix was as simple as downloading the bootable bios, burning it to a cd, entering my bios settings and enabling my cdrom as the first boot device, then rebooting and following the on-screen instructions. I haven't had a video corruption since then.
If you are truly lost at this point, i'd recommend you either do more research or take it to a professional and pay them to do it for you.
Just to clarify, this is likely an nvidia motherboard chipset (780I) problem - unlikely that the graphics card is the issue, as nvidia motherboards are known for having these types of issues. If you ask evga support to give you instructions they will, or if this is not a known issue for the 780I they will forward it to QA to work on it.